In the technical field of forming containers, hygiene is a very important issue in order to prevent any risk of contamination of the content of the containers, for example bottles with products intended to be ingested by consumers or applied on their skin. Consequently, preventing the contamination of any parts of the containers, of the hydroforming station, and of the liquid filling the containers is a fundamental issue.
As shown in FIG. 1, a typical preform 1 has a neck 3 extending along an axial direction D, which is generally vertical. The neck comprises a support ring 5 protruding radially, and a finish 7 axially opposed to the support ring.
A known type of station, such as the one shown in FIG. 1, comprises a mold 9 in which the preform 1 is placed, the support ring 5 having a first contact surface 11 in contact with a support surface 13 of the mold, with the neck protruding out of the mold.
The station also comprises an injection nozzle 15 that is movable along the axial direction D with respect to the mold 9 from a retracted position (FIG. 1), wherein the nozzle is away from the neck 3, to a work position wherein the neck 3 is received in a housing 17 defined by the injection nozzle. The housing 17 is in fluidic communication with the interior of the preform 1 and with a source 19 of the liquid to be injected into the preform. It is used for forming a container having the shape of the mold cavity. The injected liquid urges the preform 1 and expands it against the mold cavity. In its work position, the nozzle 15 abuts on an upper surface 21 of the mold 9. A drawback of such a forming station is that the injected liquid may contaminate the outside lateral screw surface of the neck.
As described in document WO-A-2013/096609, especially in its paragraph [0041] and FIG. 4, the injection nozzle may include a seal 71 arranged to lie on the finish of the preform in order to prevent any leak of liquid outside of the neck during the injection of the liquid into the preform and thus to prevent contamination of the external wall of the neck by the injected liquid.
A seal is typically a ring made of a compressible material that is softer than a surface of the nozzle on which the seal is fixed and softer than the neck when the seal is pressed against the finish. As an example, such a seal may be made of elastomeric material or silicone.
In order to achieve a high production rate of the hydroforming station, the nozzle is moved back and forth at high frequency, such as 1 Hz, from the retracted position to the work position. As the nozzle is a rather heavy part, of typically 50 kg, large forces, in the range of 3000 N, are applied on it in order to achieve these quick movements. To resist such a large axial force, the moving nozzle applies against the mold.
When the nozzle is applied upon the mold, the seal is pressed against the finish in order to provide a liquid tight sealing between the nozzle outlet and the inner volume of the preform. However, the frequency of the up and down movements may eventually damage the seal in such a way that leaks occur. Also, bits of the seal may ultimately contaminate the liquid injected in the preform. Furthermore, with such production rates, the seal has a short life duration and must be regularly replaced. During replacement, the station is idle, which reduces the production rate.
One of the aims of the invention is to provide a method for hydroforming a container that eliminates or at least reduces the leak problems, while remaining economical and enabling a high production output.